For somebody who lacks affective empathy Lydia is quite a decent (i.e. not destructive) person. She doesn't bully people, doesn't think too high of herself, doesn't cause drama just for fun, haven't committed or tried to commit any crimes. I think she is about as manipulative as gay people have to be in strictly religious countries like Saudi Arabia. She even bothered to read about deontology and utilitarianism in attempt to grok morality logically. I don't think that she has AntiSocial Personality Disorder, despite lack of empathy. After all, lack of affective empathy isn't the only trait of ASPD and it's even not trait exclusive to ASPD . She also doesn't look like having Borderline Personality Disorder or Narcissism. I wonder, what her condition could be?
I also would expect Daniel to be more cynical and experienced at recognizing manipulations, given that even normies manipulate each other.
P.S. Question for you, I hope you will answer. In the game Lydia said that there are few people about whom she really cares. Whom did she mean?